Rubbers lacking the characteristic of good processability do not band well on roll mills, extrude at slower speeds, consume more power and generate more heat upon mixing with compounding ingredients, and the like. Such rubbers require handling on a small quantity basis, which increases labor costs and reduces capacity of processing equipment. Difficult-to-process rubbers require longer processing times and higher processing temperatures. Such conditions inherently are detrimental to the quality of the uncompounded rubber, and as well to the compounded rubber, since such rubbers exhibit greater shrinkage upon cooling, higher die swell, and present undesirable characteristics such as rougher extruded stocks and increased risk of scorch.
On the other hand, rubbers that possess the characteristics of good processability exhibit converse quality, and also just as conversely represent decreased requirements for labor, time and power. Readily processable rubbers are those in which good dispersions can be obtained of all of the compounding ingredients with a minimal potential need for remill operations or use of softeners or plasticizers. Such rubbers are millable under milder conditions with less opportunity for degradation. Improved processability means better compounded stocks at lower cost.
Furthermore, if easy-to-process rubbers can be obtained on a continuous basis, this represents even further opportunity for reduced costs. Polymerization procedures operated as a continuous rather than as a batch process provide for the more economic production of more uniform compositions. Many process variables can be readily adjusted by continuous operation to optimize operations for a given polymerization recipe.